1. Field of the Invention
This invention relates in general to a developing device, a developing method, an image forming device, an image forming method and a process cartridge.
2. Description of Related Art
An image forming device, such as a copying device, a printer or a facsimile, etc., uses an electrophotographic process to form a latent image on a latent image supporter. Powder, as a developer (here, referring to toner), is adhered onto the latent image, and then the latent image is developed and visualized as a toner image. The toner image is transferred onto a recording medium or onto an intermedium transfer medium and then onto a recording medium. In this way, an image is formed.
In such a image forming device described above, there is a developing device for developing the latent image. Conventionally, toner stirred within the developing device is supported on a surface of a developing roller (a developer supporter). By rotating the developing roller, the toner is transported to a position facing the surface of the latent image supporter and the latent image on the latent image supporter is developed. After the development is finished, toner without being transferred to the latent image supporter is recycled back to the developing device by the rotation of the developing roller. The toner is stirred and charged and then transported, so that the toner is supported on the developing roller again. This technology described above is well known.
In addition, in an image forming device as disclosed in Japanese Laid Open Publication No. 9-197781 and No. 9-329947, an overlapping voltage of a DC voltage and an AC voltage is applied to between the latent image supporter and the developing roller. It is also well know that a method of a jumping development, in which the toner is transferred to the latent image supporter from a developing roller in a non-contact manner, is used to develop the latent image.
Furthermore, in an image forming device as disclosed in Japanese Laid Open Publication No. 5-31146 and No. 5-31147, an electrostatic transporting substrate is used. The toner is transported to a position facing the latent image supporter, and then the toner vibrates, floats and becomes smoke, so that the toner is separated from a transporting surface by an attractive force created between the latent image supporter and the toner and then the toner is adhered onto the surface of the latent image supporter.
However, in the image forming device with the developing device where the aforementioned developing roller is used to provide the toner to the latent image supporter, toner will intrude to between the developing roller and a side plate of the developing device. The toner rubs to cause a toner adhesion problem, etc. Therefore, the image is adversely affected. In addition, the sealing member for sealing the periphery of the developing device will degrade with time. Due to stirring and charging the developer or the toner in the developing device, the toner is scattered and the background of the image is contaminated.
In addition, when the toner is charged by friction charging or corona discharging/charging, the saturated charged toner and non-saturated charged toner are mixed, so that the charge distribution is wide. When such toner is forced to transferred to the developing roller by using a magnetic brush or a transfer roller, etc., among the toner supported on the developing roller, toner with few charges will escape at a high developing speed (a line speed of about 100 cm/sec) of the developing roller. Therefore, the toner is scattered and the background of the image is easily contaminated
Moreover, for a developing device to perform the so-called jumping development, because it has to exchange charged toner with a high voltage, a high voltage source is required, so that the device becomes large and its cost will increase.
In addition, the current problem in the image forming device using the powder (toner) is to satisfy the image quality, the cost issue and the environment problem. Regarding the image quality, when forming a color image, how to develop a single dot with a diameter of about 30 μm with a resolution of 1200 dpi is a problem, but it is preferable to develop without background contamination. In addition, regarding the cost issue, if considering a personal laser printer, not only the cost of the developing device or the developer, it is very important to reduce the total cost, including the maintenance and the final disposal cost. For the environment issue, in particular, it is very important to prevent the minute particles (toner) from being scattered within or out of the device.